The kidneys respond to changes in osmolarity by activating renin-angiotensin system. For example, when blood osmolarity is increased (low blood pressure) converting of prorenin into renin occurs in the kidneys. Renin from the circulation then stimulates the conversion of angiotensinogen, released by the liver, to angiotensin. Angiotensin stimulates the secretion of the aldosterone from the adrenal cortex which increases the reabsorption of sodium and water into the blood and stimulates the excretion of potassium (maintaining of electrolyte balance).
